1. Field of the Invention
The present invention relates to a diffraction grating array having minute diffraction gratings each arranged over a surface of a substrate for each cell and a display having a diffraction grating pattern and, in particular, to a diffraction grating array and a diffraction grating pattern-equipped display which can reproduce a correct image even when there arises any positional displacement between a light-shutting means and a diffraction grating pattern.
2. Description of the Related Art
A conventional display has often been used in which a plurality of minute cells, each comprised of a diffraction grating, are arranged over a surface of a substrate to provide a diffraction grating pattern. The method for manufacturing a display having this type of diffraction grating pattern is disclosed, for example, in JPN PAT APPLN KOKAI PUBLICATION 60-156004. This method comprises varying a minute interference fringe by a two-light interference with respect to its pitch, direction and light intensity and subjecting photo-sensitive films to a light one after another.
In recent years, another method has been disclosed in U.S. Pat. No. 5,058,992 (1991. 10. 22), according to which a display is manufactured with a given type of diffraction grating pattern formed by a plurality of minute cells (diffraction gratings) over the surface of a substrate through the movement of a substrate-mount X-Y stage under control of a computer while using, for example, an electron light exposure apparatus.
The display so manufactured uses, as a type of display image pattern having a diffraction grating pattern, an image input by an image scanner, etc., or a two-dimensional image, etc., formed by the computer graphics.
Since, however, the type of image pattern represented by the diffraction grating pattern is formed on a plane at a diffraction grating-applied substrate, only a planar (two-dimensional) type of image pattern can be represented so that a solid (3-D) image pattern cannot be displayed.
The technique of U.S. Pat. No. 5,301,062, for example, has recently been proposed by the applicant which discloses a display having a diffraction grating pattern capable of freely representing a solid (3-D) image.
With the display having this type of diffraction grating pattern, a diffraction grating constituting a cell is comprised of a plurality of groups of identical curve portions which are shifted in a parallel relation and a light-shutting means is arranged on the illumination light entry side or on the illumination light exit side of the diffraction grating and has an opening of a given configuration.
With such a display, any given intensity distribution of the illumination light is created on the diffraction grating array by the light-shutting means to determine a display pattern. Or the intensity of the diffraction light is modulated, by the diffraction grating array, through the light-shutting means to provide the intensity distribution of any diffraction light and, by doing so, to determine a display pattern.
The light-shutting means is intended to means a type which not only can render the light on and off but also can spatially modulate the light intensity at a given level. As an example of such a means, there is a liquid crystal display plate of such a type as used for an LC type television.
Generally, for the case of a cell matrix-like space light modulation element, such as an LC panel, the light modulating opening and size are made smaller than the pitch between the opening's elements and the respective opening-to-opening area is occupied by a non-light-transmissive area. In the case where the above space light modulation element is used as the light-shutting means as set out above, one opening of the space light modulation element is referred as a light-shutting element. In the case where the size of the light-shutting element is made smaller than the light-shutting element's pitch, it follows that, in the diffraction grating pattern of U.S. Pat. No. 5,301,062 above, the sizes of the light-shutting element and the diffraction grating element are made nearly equal and provide a one-to-one correspondence as shown, for example, in FIG. 5.
If any positional displacement occurs between the light-shutting element and the diffraction grating pattern, defects are produced in a diffraction direction of the diffraction light as shown, for example, in FIG. 6, thus failing to reproduce a correct image.
That is, since the identical gratings are arranged in the shift direction (normally, a vertical direction) of those curve portions of which the diffraction grating is composed, even if any positional displacement is produced, a correct image is reproduced so long as the light-shutting element is present in a range of the diffraction grating element.
However, the gratings of different inclinations are present in a parallax-produced direction (normally a horizontal direction) and, if the light-shutting element is made smaller in size than the diffraction grating element, part of the diffraction light is lacking, thus making it difficult to reproduce a correct image.
In order to reproduce such a correct image in the diffraction grating pattern as shown in FIG. 5, a strict positional alignment has to be achieved between the light-shutting means and the diffraction grating. This involves high costs and difficulty is encountered in obtaining a large-size unit.
As already set out above, with the display having a conventional diffraction grating pattern, it has been difficult to reproduce a correct image if any positional displacement occurs between the light-shutting means and the diffraction grating pattern.